The lawmakers, backed by a bipartisan group of co-sponsors, originally introduced the legislation last December amid rising fears over threats to voter registration databases and other digital systems as a result of Russian interference in the 2016 presidential election.

According to U.S. officials, Russian hackers targeted election-related systems in 21 states as part of its plot to meddle in the 2016 vote.

Since, Lankford and Klobuchar have been working with state election officials to revise the legislation. Some state officials have been wary of federal efforts to address election security, fearing a federal takeover of elections, which have historically been administered by states.

“The security of our election systems is a major national security issue, and it is appropriate for this legislation to be included in the National Defense Authorization Act,” Lankford said in a statement. “This legislation will help states prepare our election infrastructure for the possibility of interference from Russia, Iran, North Korea, or a domestic hacktivist group.”

“Election security is national security and our intelligence officials have made clear that our election systems continue to be a target for foreign adversaries,” Klobuchar said, adding, “With only 151 days until the next election, we must act now.”

The new version of the bill no longer includes a grant program designed to help states replace aging election technology due to Congress appropriating $380 million for states to use for election security in a massive funding package approved in March, an aide told The Hill.

The NDAA amendment also differs from past versions by expanding the Election Assistance Commission’s current Technical Guidelines Development Committee and renaming it the Technical Advisory Board.

This entity replaces the advisory panel originally proposed by the senators to offer states recommendations for securing their systems, which would have been housed at the Department of Homeland Security.

The amendment would also create a floor requiring states conduct post-election audits of federal elections beginning in 2020, with the option for states to waive the requirement until 2022. The measure does not, however, specify how states must go about auditing the federal results.

The Senate will take up the NDAA next week. It is not yet clear which amendments will go to the floor for a vote.

Meanwhile, the Department of Homeland Security has been working with state officials for several months to help secure their digital election systems, in some cases sending officials on the ground in states to conduct rigorous risk and vulnerability assessments.

Lankford said he is “grateful” that U.S. government agencies have worked with states to make necessary improvements but added, “This legislation is needed to help us better prepare for all election-related threats.”